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A small genus of low or procumbent evergreen shrubs, found in the colder regions of both the northern and the southern hemisphere. The number of species recognised by recent workers ranges from two (R. D. Good in Journ. Linn. Soc., Vol. 47, pp. 489-523, 1927) to eighteen (V. N. Vasiliev, in a monograph published in Russia in 1961). The only allied genus in gardens is Corema. The affinities of these shrubs are doubtful, but the general opinion now is to regard them as nearest to the box family. The generic name derives from the Greek and means ‘on rocks’. The introduced species are very hardy and easy to grow if planted in lime-free soil.